Halftoning is a process by which continuous-tone imagery are approximated on an output device (e.g., printing device) through the use of drops or dots that may vary in size, spacing, or both. The tiny halftone dots are blended into smooth tomes by the human eye. Halftoning can also be used to provide continuous-tone colors using only a limited number of discrete colors. Colors that the device cannot produce directly are simulated by using patterns of pixels in the colors available. One familiar example of halftone is the rendering of gray tones with black and white pixels, as in a newspaper photograph.
Halftoning is commonly practiced using a screening function to select the size or position of the halftone dots. Examples of screening functions are spot-function based screens, tile-based screens (such as threshold screens), or algorithmic screens (such as error diffusion screens.)